Subject: Re: [PATCH][PPPOL2TP]: Fix SMP oops in pppol2tp driver

From: James Chapman <[email-masked]>
Date: Mon, 25 Feb 2008 12:19:50 +0000

Jarek Poplawski wrote:
> Jarek Poplawski wrote, On 02/21/2008 01:08 PM:
> ...
> 
>> Another, probably simpler way would be to move almost all pppol2tp_xmit
> ...
> 
> Actually, the simplest off all seems to be now this old idea to maybe make
> sk_dst_lock globally softirq immune. At least I think it's worth of testing,
> to check for these other possible lockdep warnings. It should only need to
> change all write_ and read_lock(&sk->sk_dst_lock) in very few places:
> include/net/sock.h, include/net/ip6_route.h, and net/ipv6/ipv6_sockglue.c.
> This could be tested together with you full _bh locking patch (maybe except
> these other changes in pppol2tp_xmit).

I did this and all lockdep errors have now gone. Tests ran all weekend. 
See attached patch.

Is this an acceptable solution? If so, I'll prepare and send official 
patches.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

Index: linux-2.6.24.2/include/net/ip6_route.h
===================================================================
--- linux-2.6.24.2.orig/include/net/ip6_route.h
+++ linux-2.6.24.2/include/net/ip6_route.h
@@ -150,9 +150,9 @@ static inline void __ip6_dst_store(struc
 static inline void ip6_dst_store(struct sock *sk, struct dst_entry *dst,
 				 struct in6_addr *daddr, struct in6_addr *saddr)
 {
-	write_lock(&sk->sk_dst_lock);
+	write_lock_bh(&sk->sk_dst_lock);
 	__ip6_dst_store(sk, dst, daddr, saddr);
-	write_unlock(&sk->sk_dst_lock);
+	write_unlock_bh(&sk->sk_dst_lock);
 }
 
 static inline int ipv6_unicast_destination(struct sk_buff *skb)
Index: linux-2.6.24.2/include/net/sock.h
===================================================================
--- linux-2.6.24.2.orig/include/net/sock.h
+++ linux-2.6.24.2/include/net/sock.h
@@ -1058,11 +1058,11 @@ sk_dst_get(struct sock *sk)
 {
 	struct dst_entry *dst;
 
-	read_lock(&sk->sk_dst_lock);
+	read_lock_bh(&sk->sk_dst_lock);
 	dst = sk->sk_dst_cache;
 	if (dst)
 		dst_hold(dst);
-	read_unlock(&sk->sk_dst_lock);
+	read_unlock_bh(&sk->sk_dst_lock);
 	return dst;
 }
 
@@ -1079,9 +1079,9 @@ __sk_dst_set(struct sock *sk, struct dst
 static inline void
 sk_dst_set(struct sock *sk, struct dst_entry *dst)
 {
-	write_lock(&sk->sk_dst_lock);
+	write_lock_bh(&sk->sk_dst_lock);
 	__sk_dst_set(sk, dst);
-	write_unlock(&sk->sk_dst_lock);
+	write_unlock_bh(&sk->sk_dst_lock);
 }
 
 static inline void
@@ -1097,9 +1097,9 @@ __sk_dst_reset(struct sock *sk)
 static inline void
 sk_dst_reset(struct sock *sk)
 {
-	write_lock(&sk->sk_dst_lock);
+	write_lock_bh(&sk->sk_dst_lock);
 	__sk_dst_reset(sk);
-	write_unlock(&sk->sk_dst_lock);
+	write_unlock_bh(&sk->sk_dst_lock);
 }
 
 extern struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie);
Index: linux-2.6.24.2/net/ipv6/ipv6_sockglue.c
===================================================================
--- linux-2.6.24.2.orig/net/ipv6/ipv6_sockglue.c
+++ linux-2.6.24.2/net/ipv6/ipv6_sockglue.c
@@ -440,9 +440,9 @@ static int do_ipv6_setsockopt(struct soc
 			opt = xchg(&np->opt, opt);
 			sk_dst_reset(sk);
 		} else {
-			write_lock(&sk->sk_dst_lock);
+			write_lock_bh(&sk->sk_dst_lock);
 			opt = xchg(&np->opt, opt);
-			write_unlock(&sk->sk_dst_lock);
+			write_unlock_bh(&sk->sk_dst_lock);
 			sk_dst_reset(sk);
 		}
 sticky_done:
@@ -504,9 +504,9 @@ update:
 			opt = xchg(&np->opt, opt);
 			sk_dst_reset(sk);
 		} else {
-			write_lock(&sk->sk_dst_lock);
+			write_lock_bh(&sk->sk_dst_lock);
 			opt = xchg(&np->opt, opt);
-			write_unlock(&sk->sk_dst_lock);
+			write_unlock_bh(&sk->sk_dst_lock);
 			sk_dst_reset(sk);
 		}